mq

Manage message queues (QNX Neutrino)

Note: You must be root to start this manager.

Syntax:

mq [-d] [-m num_msgs] [-N path] [-s size] [-U string] &

Runs on:

QNX Neutrino

Options:

-d
Don't daemonize.
-m num_msgs
Set the default for the maximum number of messages, for use if the mq_attr argument to mq_open() is NULL. The default is 64 messages.
-N path
Set the pathname of the directory for message queues. The default is /dev/mq.
-s size
Set the default message size, for use if the mq_attr argument to mq_open() is NULL. The default is 256 bytes.
-U user_name
-U uid[:gid[,sup_gid]*]]
(QNX Neutrino 6.6 or later) Once running, run as the specified user, so that the program doesn't need to run as root:
  • In the first form, the service sets itself to be the named user and uses that user's groups. This form depends on the /etc/passwd and /etc/group files.
  • In the second form, the service sets its user ID, and optionally its group ID and supplementary groups, to the values provided.

Description:

The mq manager implements POSIX 1003.1b message queues. When you create a queue, it appears in the pathname space under /dev/mq.

Note:
  • The /dev/mq directory doesn't appear until you actually create a queue.
  • You can change this directory to union over the directory exported by the mqueue server by using the mq -N/dev/mqueue option, but we don't recommend this, because it may cause some user-namespace confusion.
  • Note that you can have only one of mq and mqueue running on your system at any time.

This implementation uses a queue within the kernel to buffer the messages and eliminates the context-switching overheads of using an external server (i.e., mqueue) in each message-queue operation, thus greatly improving the performance of POSIX message queues.

In order to use the mq implementation, you must link your application(s) against the libmq library. In a manual build, specify the -l mq option; in automatic/recursive builds, use this setting in your common.mk file:

LIBS += mq

For more information, see the Managing POSIX Message Queues technote.